I'm looking for advice on the best transportation to get from Heathrow to our hotel in Greenwich. We arrive on a Saturday @ 10:15am after a trans-atlantic flight and none of us are to thrilled about spending 2 hours on the tube. Is a taxi feasible and approx how much will we pay? There is 4 of us to split the fare.

A taxi could very well take as long or longer than the tube and cost your first born child. Only a SLIGHT exaggeration.

A car service would cost less than a taxi, but even a car service will be expensive since since you will be travelling all the way across London to Greenwich. If you can't bear thinking about taking the tube do book a car service.

A car service sounds like the only sensible possibility for 4. Heathrow Express would cost you £50+ to land you on the wrong side of London. The oly other possibility is a roundabout journey by bus to Feltham, train to Waterloo and then you'd have to schlep your luggage to Waterloo East for a train to Greenwich.

Thanks very much for the feedback. Any information on a reputable car company I could look into hiring?

My neighbours (we're just over the river from Greenwich) recommend a firm called Simply Airports - I think I've seen others mention them here. Phone number is (+44=UK) 20 7701 4321.

I went on the simply airports website and found the cost would be 29 pounds from the airport and 24 pounds to the airport. For 4 guys that's very affordable.
Thanks a million PatrickLondon.